Natural gas hydrate is a crystalline solid formed of gas molecules and water molecules. The ice-like solid traps the gas molecules within a cage formed by the water molecules. Natural gas hydrate is also sometimes known by other names, such as gas hydrate, gas clathrate, methane clathrate, methane hydrate, hydromethane, methane ice, and fire ice, which are all referred to herein as natural gas hydrate.
Deposits of natural gas hydrate have been found in reservoirs located under sediments on the ocean floors of the Earth. Because the natural gas hydrate is in a solid form, it cannot be easily removed from the reservoir in this state. However, if the natural gas hydrate is heated, the state of the water molecules can be changed resulting in the release of the gas molecules in a process known as dissociation. Dissociation is an endothermic process, which means that the rate of dissociation is controlled by the amount of heat available in the surrounding environment.
One technique for producing natural gas hydrate from a reservoir is to inject deeper aquifer water into the reservoir to heat the natural gas hydrate. There are several drawbacks with this technique. One drawback is that the injection of the water increases the pressure in the reservoir, thereby reducing the production rate. To avoid the increase in pressure, the natural gas hydrate water as well as the deeper aquifer water can be reduced, which greatly increases the capital and operating costs. Furthermore, the deeper aquifer water may come out of solution when injected into the natural gas hydrate reservoir, causing salts and other materials to precipitate out, which can result in blocking the reservoir, or the injecting or producing wells.